Hydraulically clamped stock feed assembly for power presses



Aug. 26,1958 J. c. DANLY ETAL 2,849,230

v HYDRAULICALLY CLAMPED STOCK FEED ASSEMBLY FOR PpwER PRESSES Filed July19; 1956 v 5 Sheets-Sheet 1 INVENTORS film-'5 C. DFiA/LY 77/EODO/PE F.NOV/9K TTORN EY Aug. 26, 195 8 J. c. DANLY ETAL HYDRAULICALLY CLAMPEDSTOCK FEED ASSEMBLY FOR POWER PRESSES 5 Sheets-Sheet 2 Filed July 19,1956 ww SQ xx O\\ KM: 1

INVENTOR 321/1455 DflA/AY 7:750 0149K IL L EFF TTORNEY Aug. 26, 1958J.'c. DANLY ,ET AL 2,849,230

HYDRAULICALLY CLAMPED STOCK FEED ASSEMBLY FQR POWER PRESSES sSheets-Shet 5 Filed July 19 1956 INVENTORS /2 75/1155 C. DAM/LY IlaVEODORE l-T A/OYHK IL fisospr TTORNEY J. C. DANLY ET AL Aug. 26, 195

HYDRAULICALLY CLAMPED STOCK FEED ASSEMBLY FOR POWER PRESSES 5Sheets-Sheet 4 Filed July 19, 1956 INVENTORS JPMEs C DEA/AV ATTORNEYAug. 26, 1958v J. c. DANLY' ET AL 9,

HYDRAULICALLY CLAMPED swocx FEED ASSEMBLY FOR POWER PRESSES Filed July19, 1956 5 Sheets-Sheet 5 v /Zo INVENTORS JEM-S C. 044 Y 77 50Q RE F,0144K Wis/Z: 6 0 B) a I ATTORNEY United States Patent HYDRAULICALLYCLAMPED STOCK FEED ASSEMBLY FOR POWER PRESSES James C. Danly, RiverForest, and Theodore F. Novak, and Vasil Georgeir, La Grange Park, 11].,assignors to Danly Machine Specialties, Inc., Chicago, 111., acorporation of Illinois Application July 19, 1956, Serial No. 598,805

11 Claims. (Cl. 271-24) Our invention relates to an hydraulicallyclamped stock feed assembly for power presses and more particularly toan hydraulically clamped stock feed assembly for power presses whichovercomes the disadvantages of power press stock feeds of the prior art.

In the prior art respective pairs of front and back feed rolls areemployed to feed continuous sheet stock through a power press which isto perform operations on the stock. The upper feed roll of each pair isspring loaded to clamp the sheet between the upper and lower rollsduring a feeding operation. With the sheet clamped, the feed rolls aredriven to advance the sheet along the press bed to the approximateposition it should occupy during a press operation. Afterthe sheet hasthus been approximately positioned, the upper rolls of the front andback feed rolls are simultaneously moved away from the lower rollsagainst the action of the spring loading means to release the sheet. Asthe press slide moves toward the sheet to perform an operation, :a pilotpin carried by the slide engages a hole formed in the sheet during apreceding operation to shift the sheet to the precise position it is tooccupy during the press operation.

In the stock feed assemblies of the prior art, a complicated andcumbersome mechanical linkage extending from front to rear of the presssimultaneously lifts the upper rolls against the action of the heavyloading springs to release the sheet to permit the pilot pin to positionthe stock exactly. In very large presses the difficulty of mechanicallylinking the lifting mechanisms for both the front and back feed rollsadds appreciably to the cost of the press.

The spring loading mechanisms of the prior art act on the respectiveends of the roll shafts to draw the upper shaft ends toward the lowershaft ends. Owing to the large loading forces, the upper and lower rollsbow in opposite directions. As a result of this bowing, the feedingforce acts only along the edges of the sheet. With this arrangement thefeed rolls wear rapidly where they engage the sheet edges and a firmfeeding force is not applied to the sheet.

We have invented an hydraulically clamped stock feed assembly for powerpresses which overcomes the disadvantages of stock feed assemblies ofthe prior art. In our assembly, a simple hydraulic system linksmechanical means for simultaneously clamping a sheet of stock betweenthe feed rolls. We avoid employing the expensive and cumbersomemechanical linkage used in the prior art. Our clamping means acts on therolls to ensure that a sheet being fed is clamped across its entirewidth, irrespective of the magnitude of the clamping force employed. -Inour system we avoid the necessity of lifting a roller against heavyloading springs.

One object of our invention is to provide an hydraulically clamped stockfeed assembly for power presses which overcomes .the disadvantages ofstock feed assemblies of the prior art.

Another object of our invention is to provide an hydraulically clampedstock feed assembly for power presses ice which avoids the use of thecumbersome mechanical lifting systems employed in feed assemblies of theprior art.

A furtherobject of our invention is to provide an hydraulically clampedstock feed assembly for power presses which ensures that a sheet ofstock being fed is gripped across its entire width between feed rollsduring a feeding operation.

A still further object of our invention is to provide an hydraulicallyclamped stock feed assembly for power presses in which the feed rollsare released without the necessity of acting against a heavy loadingforce.

Still another object of our invention is to provide an hydraulicallyclamped feed assembly for power presses which may readily be adjusted toaccommodate'various thickness of stock.

Other and further objects of our invention will appear from thefollowing description.

In general our invention contemplates the provision of a power presshaving a frame and respective pairs of front and back feed rolls, theupper roll of each of which pairs is rotatably mounted in a fixedposition on the press frame. Springs normally urge the lower roll ofeach pair to move in a direction away from the upper roll. Hydrauliclifters directly engage the lower rolls to urge them toward theirassociated upper rolls against the action of gravity and the springs. Weprovide a common hydraulic system for actuating our lifters. Thehydraulic system includes means for regulating the pressure with whichthe lifters move the lower rolls toward the upper rolls. Meansresponsive to the press operation releases the lower rolls to permit thepositioning of the sheet by the press slide pilot pin. Our assemblyincludes adjustable means for determining the limit of movement of thelower rolls away from the upper rolls. This means permits our device toaccommodate various thicknesses of stock without adding to the timerequired for the lifters to operate.

In the accompanying drawings which form part of the instantspecification and which are to be read in conjunction therewith and inwhich like reference numerals are used to indicate like parts in thevarious views:

Figure 1 is a schematic view of a power press employing ourhydraulically clamped stock feed assembly.

Figure 2 is a schematic view showing the action of the roll loadingmeans employed in stock feed assemblies of the prior art.

Figure 3 is a schematic view of a pair of feed rolls of ourhydraulically clamped stock feed assembly for power presses showing theclamping action of a pair of feed rolls.

Figure 4 is a schematic view of our hydraulically clamped stock feedassembly for power presses.

Figure 5 is a sectional view of a lower feed roll and one of ourlifters.

Figure 6 is a sectional view of one of our hydraulic lifters taken alongthe line 6-6 of Figure 5.

Figure 7 is an end elevation of the actuating means for the stockthickness adjustment of our hydraulically clamped stock feed assemblyfor power presses taken along the line 77 of Figure 4 and drawn on anenlarged scale. Figure 8 is a sectional view of a bleed-off valveemployed in our hydraulic system to permit opening and closing of thefeed rolls of our hydraulically clamped stock feed assembly for powerpresses at any point in the press operation.

Referring now more particularly to Figure 1 of the drawings, a powerpress indicated generally by the reference character 10, with which ourstock feed assembly is used, includes an inner slide 12 adapted to bevertically reciprocated on the press frame in a manner known to the artto perform operations on a sheet 14 of stock being fed through thepress. Sheet 14 passes between a pair of respective upper and lowerfront feed rolls 16 and 18 and a pair of respective upper and lower rearfeed rolls 20 and 22. When the sheet 14 is to be fed, the respectivepairs of rolls 16 and 18 and 20 and 22 are moved to clamp sheet 14between the upper and lower rolls. This is accomplished in a manner tobe described hereinafter. The feed rolls 16, 18, 20 and 22 are driven tolocate sheet 14 in the approximate position it should occupy during anoperation of the press. After the sheet is thus approximately located,the feed rolls are released in a manner to be described and slide 12moves downward, as viewed in Figure 1, toward the work. In the course ofthis movement, a pilot pin 24 carried by slide 12 engages a hole 26formed in the sheet during a previous operation of the press by a punchor the like 28. It will be seen that pilot pin 24 is longer than thepunch 28, with the result that it engages hole 26 accurately to positionsheet 14 before the punch 28, carried by slide 12, engages the work. Itwill be appreciated that both the front rolls 16 and 18 and the rearrolls 20 and 22 must be released together if pilot pin 24 is to positionsheet 14 accurately.

Referring now to Figure 4, our hydraulically clamped stock feed assemblyincludes a stationary front frame member 30 provided with a pair ofspaced upright hearing supports 32 and 34. We rotatably mount the shaft36 of the front upper feed roll 16 in bushings 38 and 40 carried by therespective supports 32 and 34. Respective guideways 42 and 44 formed inthe supports 32 and 34 guide bearing blocks 46 and 48. We rotatablymount the shaft 50 of the lower front feed roll 18 in respectivebushings 52 and 54 carried by blocks 46 and 48. We thread repectivepairs of elongated studs 56 and 58 into the undersides of blocks 46 and48. These studs extend through suitable openings 61) in frame member 30.Respective pairs of nuts 62 and 64 on the ends of the pairs of studs 56and 58 retain respective washers 66 and 68 on the studs. Respectivepairs of springs 70 and 72 on the shanks of the pairs of studs 56 and 58bear between Washers 66 and washers 68 and the underside of member 30.From the foregoing, it will be apparent that the springs 70 and 72 actto move the lower roll 18 away from the upper roll 16.

We provide hydraulic lifters, indicated generally by the referencecharacter 74, for moving the lower roll 18 upwardly against the actionof springs 70 and 72 to clamp a sheet of work being fed between rolls 16and 18.

Referring now to Figures 4 to 6, each of these lifters 74 includes apiston 76, the base 78 of which is secured to the upper surface ofmember 30 by means such as bolts 80. A respective cylinder 82 cooperateswith each of the pistons 76 to provide a space 84 into which fluid underpressure may be admitted to cause relative movement between the piston76 and its associated cylinder 82. A seal 86 prevents escape of fluidfrom the chamber 84. We form each of the cylinders 82 with a first pairof spaced arms 88 and 90 extending perpendicularly in one direction fromthe axis of the lower feed roll 18. A second pair of spaced arms, onearm 92 of which is shown, is formed on each of the cylinders 82. Thepair of arms including the arm 92 extends in the opposite direction fromthe pair of arms 88 and 90. A shaft 94 is supported between the arms 88and 90. Bearing elements 96 rotatably mount a roller 98 on shaft 94. Wemount a second roller 100 on hearing elements 102 disposed betweenroller 108 and a shaft 104 extending between the pair of arms includingarm 92. The disposition of the respective rollers 98 and 100 is suchthat these rollers engage the lower feed roll 18 of the front feedrolls. Springs 70 and 72 normally urge lower roll 18 to seat it on therespective rollers 98 and 100 carried by the hydraulic lifters 74.

We form each of the pistons 76 with a bore 106 through which fluid underpressure is admitted to the corresponding chamber 84.- A plurality offittings 108 connect respective fluid feed pipes 110 to the bores 106.Pipes 110 pass through bores 112 in frame member 30. When fluid underpressure is supplied, in a manner to be described, to the pipes 110; itpasses through the pipes and through the bores 106. into the chambers 84to move cylinders 82 and the lower feed roll 18 supported by thecylinders, upwardly against the action of springs 70 and 72 to clamp asheet 14 of material beingfed between the lower roll 18 and the upperroll 16.

Referring again to Figure 4, shaft 36 carries for rotation with it agear 114 which is driven by a gear 116 to advance the sheet being fed.Gear 116 is intermittently driven in a manner known to, theart to feedthe sheet 14 a predetermined distance into the press.

The rear feed roll support frame includes a member 1.18 and a pair ofrespective upright supports 120 and 122. We rotatably mount the shaft124' of the rear upper feed roll 20 in respective bushings 126 and 128carried in supports. 120 and 122. A gear 130 carried by shaft 124 forrotation with it is driven by a gear 132 to drive shaft 124 insynchronism with shaft 36, in a manner known to the art, to advance asheet being fed.

We form the supports 120 and 122 with respective slots or guideways 134and 136. We rotatably mount the shaft 138 of the lower feed roll 22 inbushings 140 and 142 carried by support blocks 144 and 146 disposed inguideways 134 and 136. We thread a first pair of respective studs 148 inthe underside of block 144. Studs 148 pass through openings 150 inmember 118. Washers 152 are retained on studs 148 by nuts 154. Springs156 carried by the shanks of studs 148 bear between the washers 152 andthe underside of member 118.

We thread a second pair of respective studs 158 into the underside ofblock 146. Studs 158 pass through openings 160 in member 118. Washers162 held on studs 158 by nuts 164 retain springs 166 on the shanks ofthe studs. Springs 166 bear between washers 162 and the underside ofmember 118. From the foregoing it will be seen that springs 156 and 166normally urge the lower roll 22 to move in a direction away from theupper roll 20.

Our rear feed roll assembly includes a plurality of hydraulic liftersindicated generally by the reference character 168. These lifters 168are identical with the lifters 74 and are bolted or are secured by otherconvenient means to the member 118. Respective fluid feed pipes 170 arearranged to supply fluid under pressure to the chambers of the lifters168. The rollers 98 and 100 of the lifters 168 are disposed to supportthe lower feed roll 22 of the rear feed rolls. When fluid under pressureis supplied, in a manner to be described, to the pipes 170, lifters 168move the roll 22 against the action of springs 156 and 166 upwardlytoward roll 20 to clamp a sheet 14 being fed between the rolls 22 and20.

Still referring to Figure 4, our fluid pressure system includes areservoir 172 which contains a supply of a suitable fluid, such as oilor the like. A check valve 174 permits fluid to flow from the tank orreservoir 172 to a fluid supply pipe 176. A pipe 178 connects supplypipe 176 to a pipe 180 which conveys fluid to respective manifold pipes182 and 184 which supply fluid to the pipes 110 connected to lifters 74and to the pipes 178 connected to lifters 168. We provide means fordisplacing the fluid in the system in synchronism with operation of thepress to move lower rolls 18 and 22 simultaneously to clamping positionwhen the sheet 14 being fed is to be advanced, and to release the lowerrolls when a press operation is to be performed. A shaft 185 carried acam 183 for rotation with it by means of a key 186. A cam followercarried by the free end of an arm 192 engages the surface of cam 188. Apin, or the like, 194 pivotally supports arm 192 on the press frame. Apipe 196 connects the pipe 176 to a stationary cylinder 198. A piston200 disposed within cylinder 198 has a rod 202 which pivotally engages apin 204 on the arm 192. A spring 206 in cylinder 198 normally urgespiston 200 to the left, as viewed in Figure 4, to urge follower 190 intoengagement with the surface of cam 188. When, under the action of thepress drive, shaft 185 rotates in the direction of arrow A, a high point208 on cam 188 pivots arm 192 in a clockwise direction, as viewed inFigure 4, to move piston 200 to the right against the action of spring206. This action displaces the fluid in the system to drive the fluid,such as oil, into the chambers 84 of all of the lifters 74 and 168.Under the influence of this fluid all the cylinders 82 move upwardly tolift lower rolls 18 and22 to clamp the sheet 14 between the upper andlower rolls of the front and rear feed rolls. Gears 114 and 130 aredriven to advance the sheet. During the period of advance of the sheet,cam 188 continues to rotate and is so shaped that it continues todepress piston 200 beyond the position to which it is moved when thehigh point 208 of cam 188 engages follower 190, thus providing anadditional supply of fluid to replace losses due to leakage.

It is a recognized fact in the art that no hydraulic system iscompletely leakproof. Some fluid will escape from our system during thefeeding operation. In order to maintain the clamping pressure of ourfeed rolls substantially constant during a feeding operation, we mustreplace or otherwise account for fluid which escapes. We form thesegment of cam 188 between the high point 208 and the end 210 of thehigh surface, with'a gradually increasing radius. Thus, as the camrotates in the direction of the arrow A, piston 200 is gradually movedfurther to the right to account for oil which leaks from the system andto maintain the clamping pressure of the feed rolls. When cam 188 hasrotated to a point where the end i 210 of the high surface passesfollower 190, spring 206 moves piston 200 to the left, as viewed inFigure 4, to relieve the hydraulic pressure and to permit springs 70 and72 and springs 156 and 166 to move the lower rolls 18 and 22 away fromthe upper rolls to unclamp the sheet of stock being fed. In thiscondition of the system, fluid may flow from tank 172 through checkvalve 174 into the system-to replace oil lost by leakage during thefeeding operation just completed.

In order that the clamping pressure shall not exceed a predetermineddesired pressure, we connect an adjustable relief valve indicatedgenerally by the reference character 212 between pipe 176and tank 172.We connect an opening 216 in the end of housing 214 of valve 212 to pipe176. A pipe 220 connects an opening 218 in the housing side to tank 172.Opening 216 is formed to provide a seat for a ball 222 disposed withinhousing 214. A spring 224 bears between the ball 222 and an adjustingmember 226. Member 226 includes a shaft 228 threaded in the end ofhousing 214 remote from opening 216. The pressure with which spring 224retains ball 222 in its seat may be adjusted by turning a knurled knob230 formed on shaft 228. This pressure is adjusted to a predeterminedpressure. If the pressure within the system exceeds this predeterminedpressure, oil moves ball 222 away from its seat against the action ofspring 224 and flows back into tank 172 through pipe 220. It will beappreciated that this adjustable relief valve affords a means forregulating the pressure in-the system to ensure that sheets of stock ofdifierent thicknesses are clamped with the same pressure.

From the foregoing, it will be seen that a sheet 14 being fed is clampedduring the period of time when roller 190 rides on the high portion ofthe surface of earn 188. The sheet i released when the follower 190rides on the low portion of this surface. We provide means for manuallyreleasing the sheet 14 by relieving the clamping pressure of the lowerrolls 18 and 22.

Referring to Figures 4 and 8, a pipe 232 connects the pipe 178 to amanually operable bleed-off valve indicated generally by the referencecharacter 234. Pipe 232 conducts fluid under pressure to the interior ofthe housing 236 of valve 234. A piston 238 disposed within housing 236is formed with a threaded rod 240 disposed in a threaded bore 242 in aplate 244 secured over the open end of housing 236 by bolts 246. A handWheel 248 formed with a. knob 250 provides a means by which rod 240 maybe turned ,to move piston 238 within housing 236. In normal operation ofthe system, piston 238 is in it extreme left-hand position withinhousing 236, as viewed in Figure 8. When follower is on the high portionof cam 188 o that rolls 18 and 22 are in clamping position and it isdesired to release the sheet 14, wheel 248 is turned to shift piston 238to the right, as viewed in Figure 8, to permit more fluid to flow intohousing 236. When this is done, the springs 70, 72, 156, and 166 moverolls 18 and 22 away'from the rolls 16 and 20 to force fluid intohousing 236. The system may again be rendered operative by turning wheel248 to'move piston 238 to the left, as viewed in Figure 8, to return theoil in housing 236 to the system. For convenience we connect a pressuregauge 252 to pipe 178- to indicate the pressure in the system,

Referring again to Figures 4 to 7, each of the pistons 76 of the lifters74 is formed with a bore 254 through which a shaft 256 passes. We formeach of the shaft portions at a lifter 74 with a pair of spacedeccentrics 258 and 260. These eccentrics 258 and 260 determine thebottom limit position of the cylinders 82. As has been explainedhereinabove, when the hydraulic system is in a condition in which fluidpressure is permitted to flow out of the chambers 84 of the lifters 74,springs 70 and 72 move roll 18 and the roll supporting cylinders 82downwardly. The arrangement of our lifters is such that the bottomposition of each of the cylinders 82 isdetermined by the eccentrics 258and 260. As can be seen by reference to Figure 6, when fluid ispermitted to flow out of a chamber 84 of a lifter 74, the cylinder 82moves downwardly until its underside 262' engages the eccentrics 258 and260. As shaft 256 is rotated about its axis, eccentrics 258 and 260rotate about this axis to change the bottom limit position of thecylinder 82 of a lifter 74.

We provide means for positioning shaft 256 about its axis to move theeccentrics 258 and 260 to regulate the bottom limit position ofcylinders 82. In this manner we are able to maintain constant the lengthof the working stroke of the cylinders for sheets of stock of variousthicknesses; We thus eliminate waste motion which otherwise would existwhere thin sheets were being fed. The rear feed roll assembly, includingfeed rolls 20 and 22, includes a shaft 280 similar to the shaft 256 andformed with eccentric portions 288 and 260 for determining the bottomlimit position of the rear lower feed roll 22. We provide respectiveassemblies indicated generally by the reference characters. 269 and 282for positioning shafts 256 and 280 to determine the bottom limitpositions of rolls 18 and 22. Referring to Figure 7, we have shown thedetails of the assembly 282. The assembly 269 is similar to the assembly282, and so will not be described in detail.

Referring to Figures 4 and 7, shaft 280 extends outboard through abracket 264 carried by frame member 118. Bracket 264 carries a plate 266provided with a plurality of locating holes 268 arranged in a circleabout shaft 280. The outboard end of shaft 280 carries for rotation withit a crank 270, one end of which supports a spring loaded locating pin272 formed with a knob 274. Eccentrics 258 and 260 may be positioned asdesired by lifting the locating pin 272 out of a hole 268 and rotatingcrank 270 to the proper position and permitting the pin 272 to drop intothe hole 268 in that position. For convenience in determining theposition of the eccentrics, crank 270 is provided with a 7 pointer 276which cooperates with. a scale 278 calibrated in terms ofstockthiekness, or the like.

In operation of our hydraulically clamped stock feed assembly, where anew sheet of stock is to be fed to the press, the cranks or de tent arms270 of the respective assemblies 269 and 282 first are rotated to aposition corresponding to the full open position of the front feed rolls16 and 18 and of the rear feed rolls 20 and 22. It will be understoodthat the valve 234 is in its full open position to bleed oif oil fromthe system. Springs 70 and 72 and 156 and 166 urge the respective lowerfeed rolls 18 and 22 to their furthest position away from rolls 16 and20. The cylinders 82 of the respective units 74 and 169 rest oneccentrics 258 and 260 which are then in their lowest position, owing tothe fact that the arms 270 are in the full open position. The sheet ofstock is then introduced between the front feed rolls 16 and 18. Toinitiate the feeding action, the valve 234 is closed to return oil tothe system to render the system operative. The crank arm 270 of theassembly 269 is rotated to position eccentrics 258 and 260 associatedwith lifters 74 to determine the bottom limit position of cylinder 82 ofthese units. This bottom limit position corresponds with the thicknessof stock being fed.

After these front feed rolls 16 and 18 have been closed to clamp a sheetof stock between them, the press is run and gear 114 drives upper feedroll 16 or lower feed roll or both to advance the sheet through thepress. This feeding motion of the sheet is continued until the sheet ofstock enters between the rear feed rolls 20 and 22. Conveniently at thispoint the press is stopped in a manner known to the art so that rolls 16and 20 no longer are driven. In order to close the rear feed rolls 20and 22, the valve 234 first is opened to release the stock from the feedrolls. This permits the sheet being fed to be properly positioned withrespect to the rear feedrolls 20 and 22. Valve 234 is again closed andlower feed rolls 18 and 22 move up toward upper feed rolls 16 and 20. Itwill be remembered that the bottom limit position of roll 18 already hasbeen regulated for the thickness of stock being fed. The arm 270 of theunit 282 is rotated to regulate the bottom limit position of roll 22 inaccordance with the thickness of the stock being fed. The sheet of stockis now ready to be operated upon by the press and can be fedautomatically by our system through the press.

In normal operation of our system shaft 185 drives cam 188 properly tosynchronize the clamping and feed operations of the front and rear feedrolls with the press slide movement. When an operation is to beperformed by the press slide, roller 190 engages the low portion of cam188, with the result that piston 200 occupies its left-hand position asviewed in Figure 4, to permit some of the fluid within the system toenter housing 198. In this condition of the fluid system, rolls 18 and22 are urged to their bottom limit positions determined by the positionsof cranks 270. The sheet being fed is free to be accurately located bythe pilot pin 24 engaging in a hole 26 previously formed in the sheet.When the press slide completes its operation, point 208 on cam 188engages roller 190 to drive piston 200 to the right, as viewed in Figure4, to displace the fluid in housing 198 into the system. The fluid flowsinto the chambers 84 of lifters 74 and 168 to raise lower rolls 18 and22 to clamp the sheet being fed between the front and rear pairs of feedrolls. The feed rolls 16, 18, 20 and 22 are driven to advance the sheetthrough the press approximately to position it for the next operation ofthe press slide 12. When the sheet is thus approximately positioned,roller 190 passes point 210 of cam 188 and lower feed rolls 18 and 22again are spring urged downwardly, as viewed in Figure 4, to force fluidinto housing 198. The sheet 14 is again released and may be positionedfor the next press operation by pilot pin 24 as slide 12 descends. It

will be remembered that cam 188, between points 208 and 210 as the camtravels in the direction of the arrow A, is formed with a graduallyincreasing radius which accounts for fluid which may lead out of thesystem. Valve 212 provides a relief for the system in the event pressureexceeds a determined pressure. This valve may be actuated to ensure thatthe same clamping pressure is exerted on sheets of stock of differentthicknesses. As has been explained hereinabove, valve 234 provides ameans by which fluid may be bled off from the system to release thesheet at any point in the press operation.

Referring now to Figure 2, the feed roll clamping means of the prior artexerts at corresponding ends of the shafts 284, and 286 of a pair offeed rolls 288 and 290 a pair of opposed forces indicated by arrows Band C. Similar forces indicated by arrows D and E are exerted on theother pair of corresponding ends 292 and 294 of the rolls 288 and 290.As can be seen by reference to the figure, these forces cause the rolls288 and 290 to bow, with the result that the force with which the rollsgrip a sheet 296 of material being fed is exerted only at the edges ofthe sheet. This requires a heavy clamping force. It renders feeding ofthe sheet uncertain and causes excessive roll wear at the points wherethe rolls engage the sheet edges.

Referring to Figure 3, we have shown the action of our hydrauliclifters, such, for example, as the lifters 74, on the front feed rolls16 and 18. As can be seen by reference to the figure, our lifters, ofwhich we have shown three by way of example, act directly on the surfaceof the lower roll 18 against the action of the springs 70 which act onthe roll ends. While, under the action of our lifters 74, lower roll 18may bow, upper roll 16 will bow in the same direction, with the resultthat the rolls engage the sheet 14 being fed across its entire width.This operation overcomes the disadvantage inherent in the oppositelybowing feed roll assemblies of the prior art.

It will be seen that we have accomplished the objects of our invention.We have provided an hydraulically clamped feed roll assembly for powerpresses which overcomes the disadvantages inherent in the feed rollassemblies of the prior art. Our assembly includes a simple hydraulicsystem which links the front and rear feed roll assemblies. The clampingmeans of our system need act only against gravity and relatively lightspring pressure. Our system readily accommodates stock sheets ofdifferent thicknesses while providing means for clamping all sheets withthe same pressure. Our system includes an adjustment for ensuring thattime is not wasted in operating our clamping means where thin sheets arebeing fed. Our clamping means ensures that a sheet of stock being fed isgripped across its entire surface during a feeding operation.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of ourclaims. It is further obvious that various changes may be made indetails within the scope of our claims without departing from the spiritof our invention. It is therefore to be understood that our invention isnot to be limited to the specific details shown and described.

Having thus described our invention, what we claim is:

1. In a power press through which a sheet of stock is to be fed, a stockfeed assembly including a pair of first feed rolls including an upperroll and a lower roll, means normally urging said upper and lower firstfeed rolls away from each other, fluid means for moving said upper andlower first feed rolls toward each other against the action of saidmeans normally urging the rolls, a pair of second feed rolls includingan upper roll and a lower roll, means normally urging said upper andlower second feed rolls away from each other, fluid means urging saidupper and lower second feed rolls toward each other against the actionof the means normally urging the second feed rolls away from each otherand a. common fluid system for supplying fluid under pressure to saidfluid means.

2. A stock feed assembly as in claim 1 in which said fluid systemincludes a supply of fluid under pressure, means including a first checkvalve for connecting said supply to said fluid means, means responsiveto the operationof said press for displacing the fluid in said system toactuate said fluid means to act against the respective means urging thelower first roll and the lower second roll away from the upper firstroll and upper second roll.

3. A stock feed assembly as in claim 1 in which said fluid systemincludes a supply of fluid, a cam adapted to be driven in synchronismwith the operation of the press and means actuated by said cam fordisplacing fluid from said supply to said fluid means.

4. A stock feed assembly as in claim 1 in which said fluid systemincludes a supply of fluid, a cam adapted to be driven in synchronismwith the operation of said press, and means actuated by said cam fordisplacing fluid from said supply into said fluid means, said cam havinga first portion for actuating said displacing means to supply fluidunder pressure to said fluid means, a second portion having a graduallyincreasing radius in the direction of cam rotation and a third portionpermitting fluid to flow from said fluid means.

5. A stock feed assembly as in claim 1 in which said fluid systemincludes a supply of fluid, means responsive to the press operation fordisplacing fluid from said supply to said fluid means and a bleed-01fvalve for relieving the pressure in the system.

6. A stock feed assembly as in claim 1 in which said fluid systemincludes a reservoir of fluid, a first check valve for supplying fluidfrom said reservoir to the system and a second adjustable check valvefor permitting fluid to flow from said system to the reservoir when thei system pressure exceeds a predetermined pressure.

7. In a power press through which a sheet of stock is to be fed, a stockfeed assembly including an upper feed roll and a lower feed roll, meansnormally urging said upper and lower feed rolls away from each other,fluid means for moving said upper and lower feed rolls toward each otheragainstthe action of said means normally urging the rolls, a supply offluid under pressure, means including a first check valve for connectingsaid supply to said fluid means, and means responsive to the operationof said press for displacing the fluid in said system to actuate saidfluid means to act against the means urging the upper and lower feedrolls away from each other.

8. In a power press through which a sheet of stock is to be fed, a feedroll assembly including an upper and a lower feed roll, means mountingsaid rolls for relative movement toward each other to clamp said sheet,means normally urging said rolls away from eachother and fluid meanscomprising rollers for engaging, the surface of the lower roll foracting against said means normally urging said rolls to clamp saidsheet.

9. In a power press through which a sheet of stock is to be fed, a feedroll assembly including an upper and a lower feed roll, means mountingsaid rolls for relative movement toward each other to clamp said sheet,means comprising a spring normally urging said lower roll away from saidupper roll and fluid means comprising rollers in engagement with thesurface of said lower roll for acting against said spring to clamp saidsheet between said rolls.

10. In a power press through which a sheet of stock is to be fed, a feedroll assembly including a frame, an upper feed roll, means rotatablymounting said upper feed roll on said frame, a lower feed roll, meansrotatably mounting said lower feed roll on said frame for movementtoward and away from said upper feed roll, means including a spring forurging said lower feed roll away from said upper feed roll, fluid meansfor moving said lower feed roll toward said upper feed roll against theaction of said spring and adjustable means for limiting the movement ofsaid lower feed roll away from said upper feed roll.

11. In a power press through which a sheet of stock is to be fed, a feedroll assembly including a frame, an upper feed roll, means rotatablymounting said upper feed roll on said frame, a lower feed roll, meansrotatably mounting said lower feed roll on said frame for movementtoward and away from said upper feed roll, means including a spring forurging said lower feed roll away from said upper feed roll, a pistoncarried by said frame, a cylinder to which fluid under pressure may befed to displace said cylinder with respect to said piston, a shaftformed with an eccentric, said cylinder adapted to engage said eccentricto limit the movement of said lower feed roll away from said upper feedroll and means for rotating said shaft to adjust the bottom limitposition of said lower feed roll.

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